Intraocular lens (IOL) implantation to treat cataracts and aphakia is one of the most common surgical procedures performed, with an estimated 3 million surgeries per year in the United States and millions more worldwide. As a result, the industry is rapidly growing, with new IOL designs and materials emerging each year. Since the emergence of the simple glass monofocal IOLs, more flexible materials have been introduced having more complex optical capabilities, such as toric and multifocal lenses.
To accommodate this constantly evolving field, the development and investigation of innovative standard test methods for precise and objective evaluation of IOL optical properties is important. To effectively accomplish this goal, critical optical properties that affect the safety and efficacy of IOLs need to be identified and targeted. These properties include dioptric powers, reflected glare, imaging quality, and light glistenings.
Furthermore, environmental parameters that influence optical properties need to be quantitatively evaluated (e.g. conical temperature, contaminants, properties of surrounding media, and exposed light). Research is ongoing to systematically assess how changes in the environmental parameters influence critical optical properties. As an example, changes in IOL surface temperatures can result in significant changes in dioptric powers, astigmatism, and spherical aberrations. Additionally, changes in environmental parameters are largely dependent on the IOL designs themselves. For example, the angular edge design of some IOLs has been found to produce unwanted glare.
Approximately 30% of patients in need of cataract surgery also have more than 1.50 D of corneal or refractive astigmatism. Toric IOLs were introduced to correct these corneal astigmatisms and provide different optical properties in comparison with the more basic spherical IOLs. The toric IOLs produce two dioptric powers (spherical equivalent, SE; and cylinder, C) by including an asymmetrical lens aligned orthogonally to a spherical lens. The cylinder power is lower than the spherical equivalent and is designed to reduce mild to moderate astigmatism. The additional unique dioptric power properties introduced by toric IOLs means that additional requirements are needed to properly evaluate their safety and efficacy. For example, to accommodate the new plane of focus of toric IOLs, tick marks are used to indicate the anterior cylinder axis. The accuracy of aligning the tick marks during implantation can significantly influence the efficacy of the IOL and as a result, high precision is required. Occasionally the IOL will need to be re-aligned a few weeks after the primary implantation.